1. Field of the Invention
The present invention relates to a core structure of corrugated fins of a heat exchanger having tubes through which coolant flows being fixed to seat plates, the core structure of corrugated fins used for a heat exchanger such as a radiator for a vehicle or the like.
2. Description of the Related Art
A core structure of a conventional heat exchanger is, for example, disclosed in Japanese Patent Laid-open No. Tokkaihei 11-14285 and in Japanese Patent Laid-open No. Tokkaihei 9-318292. This core structure of a conventional heat exchanger has seat plates arranged opposite to each other with a predetermined space interposed therebetween, tubes and corrugated fins arranged alternately between the seat plates, and reinforcements which couple and reinforce both end portions of the seat plates.
FIG. 10 shows an example of the core structure of the conventional heat exchanger. As shown in FIG. 10, two seat plates 101 are coupled and reinforced at their both end portions by reinforcements 104, and tubes 102 and corrugated fins 103 are alternately arranged between the seat plates 101.
Further, as shown in FIG. 11, on the seat plates 101, tube holes 105 for fixing the tubes 102 by insertion and connection portions 106 having wall portions slanting toward the tube holes 105 are formed by burring.
On the other hand, in recent years, as the tubes 102, tubes having partitions 104 inside as shown in FIG. 12 have become the mainstream. Examples of these tubes are disclosed in Japanese Patent Laid-open No. 2002-303496 for example.
Further, seat plates and tubes in recent years are desired to be made thinner in order to improve a heat exchange rate of a heat exchanger.
However, in the core structure of the conventional heat exchanger, when coolant flowing from an engine into a radiator rapidly changes in temperature from low to high as will be described later, large thermal expansion of the tubes 102 and the seat plates 101 occurs, which may cause the connection portions 106 to press the tubes 102 to crack/break root portions of the tubes 102. This has been an obstruction to make the seat plates 101 and the tubes 102 thinner.
Further, since the tubes 102 in which the partitions 104 are formed have a particularly small allowable amount of deformation against an external pressure, a countermeasure has been urgently needed against thermal stress applied by the connection portions 106 of the seat plates 101 to the tubes 102.
Here, the rapid change of coolant flowing from an engine into a radiator in temperature from low to high occurs, for example, in a case when an engine is started in a cold region. In this case, a state that coolant of the engine increases gradually in temperature but does not flow into a radiator continues until it reaches a valve-opening temperature of a thermostat, and then the temperature of the coolant becomes high enough to cause a valve of the thermostat to open, so that the coolant of high temperature flows into the radiator for the first time, or in a case that a so-called hunting phenomenon occurs such that a thermostat repeats opening and closing when driving in a cold region.
The present invention has been made in light of the above-described problems, and an object thereof is to provide a core structure of a heat exchanger capable of preventing a crack and a breakage of root portions of tubes fixed to seat plates due to thermal stress of the seat plates against the tubes when coolant flowing from an engine into a heat exchanger, such as a radiator, rapidly changes in temperature from low to high.